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Background

Current projections of the impacts of climate change on forested ecosystems rely heavily on models that relate the distribution of climate variables such as precipitation and temperature to the distribution of forest species. The impacts of climate change are typically projected as extrapolations of these relationships given predicted changes in climate. While there is consensus in the scientific community that temperatures will increase in the next century, relatively little certainty exists about the variability in this increase, its rate, or accompanying changes in precipitation. In the western United States, this uncertainty is further compounded by the topographic complexity introduced by a mountainous biophysical setting. In addition, ecosystems in the West are influenced by climate variability driven by periodic sea-surface temperature anomalies in the Pacific Ocean. The El Niño/Southern Oscillation
(ENSO) and the Pacific Decadal Oscillation (PDO) have been shown to have strong influences on precipitation in the West. The interaction of climate change and climate variability in the complex terrain of the west makes projection of climate change impacts on forests complicated.

In this study, we propose a case study designed to examine the spatial and temporal variability of climate impacts on an ecological process. Specifically, we aim to understand how variability in Douglas-fir growth rates varies with scale-dependent, spatiotemporally variable limiting factors. The purpose of the study is to go beyond current correlational models and dendroecology and instead develop ecophysiologically-informed, mechanistic predictions of Douglas-fir growth rate responses to climate change and climate variability.

Research Questions

What climate variables are most important to Douglas-fir growth rates?

What is the biogeographical variability in this sensitivity? What is the temporal variability in this sensitivity?

Is this variability in sensitivity related to changes in the relative importance of multiple limiting factors? At what levels of hierarchical organization (tree, watershed, region)?